It depends on the field of biology. If you want to study bugs and things, you could get by with no math. I’d avoid fields such as population genetics. Most of molecular biology is quite biochemical and so requires doing a lot of simple calculations, but it’s more arithmetic than mathematics. So there can be a lot or none. It’ll depend on what sort of biology you would like to do. Also, computers are our friends.
we’ve had just one semester (plus one obligatory and one voluntary semesters of physics) and that was it. And I still live and do some biochemistry. But honestly, I could use some more of real statistics or this stuff.
In my field (cellular & molecular biology, biotechnology), in practice, vast majority of maths involves calculating correct concentrations, cell numbers, molarities and other fairly basic stuff based on established formulas. When analyzing results you need also a degree of maths to calculate your p values and such, but statistical programs do most of the hard math on your behalf. During my university studies most of the tricky maths was in the biochemistry and especially chemistry classes.
So, in a nutshell, I’d say biology is not very maths intensive field but a good command of maths certainly won’t hurt you.
However, if you ‘struggle a lot’, then that might be a problem. Why don’t you borrow some university biochem textbooks or such and see how you do with the calculations? In my experience, high school maths should be enough for most of them, since few bio degrees have any proper maths courses included — you mostly use high school maths in the university as well (there may be regional differences, of course).
Oh, just noticed I used the term ‘maths’ all the time. Hope you bear with me!